为了防止静电危害。下列措施中不当的是
A:油罐车上拖一条与地面接触的铁链
B:飞机的机轮上装有搭地线或用导电橡胶做轮胎
C:在地毯中夹杂不锈钢纤维
D:尽可能保持印染厂空气干燥
正六边形的边心距与边长之比为( )
I have three stamps, one is from Canada, one is from America, ___ is from China.